Ginny spends some time describing the present she got Harry for his 17th birthday.
"I couldn't think what to get you," she said.
"You didn't have to get me anything."
She disregarded this too.
"I didn't know what would be useful. Nothing too big, because you wouldn't be able to take it with you."
"So then I thought, I'd like you to have something to remember me by, you know, if you meet some Veela when you're off doing whatever you're doing."
(Deathly Hallows, Chapter 7, The Will of Albus Dumbledore).
Yet she doesn't actually say what she got him.
What was the small, useful and memorable gift she got him for his birthday? Or did she not find him anything?